1. Field of the Invention:
The present invention relates to a millimeter-wave, fin-line, passive, gas discharge device operable as a radar receiver protector. This gas discharge device utilizes; a hermetically sealed, gas filled housing, a radioactive primer and two parallel, bevelled, tapered fins to produce an electrical gas discharge thereby protecting a radar receiver by blocking an incident radio frequency signal. Broadband and narrow band embodiments are described utilizing inert and reactive gases in the vacuum sealed housing.
2. Description of the Prior Art:
A receiver protector is well known in the prior art and many examples of this art may be found in United States patents.
The U.S. Pat. No. 2,972,083 issued Feb. 14, 1961 to inventor R. M. Walker et al. entitled "Sealing Waveguide Window", detailed a window for use with hermetic, high-vacuum type seals for the controlled propagation of electromagnetic energy in waveguides. This invention did not claim the use of an inert gas and radioactive primer with bevelled fin point discharge effectively stopping incident, millimeter wave, electromagnetic energy. An iris utilizing a gap electrode within the waveguide functioned as a transmit/receive "switch".
The patent to L. W. Roberts, U.S. Pat. No. 3,O72,865, issued Jan. 8, 1963 for a "Gaseous Discharge Device". This patent described a wideband, high frequency, gaseous discharge device or tube having sealed waveguide sections, and one or more resonant structures. This improved electrode structure supplied residual electrons adjacent to a discharge gap with a "keep alive" electrode structure comprising titanium tipped pellets. This device did not describe the fin-line housing, radioactive primer, bevelled fin-line gap critical to this application discharge. Further, the L. W. Roberts patent did disclose a waveguide structure operable in the wideband region providing a gaseous discharge over a narrow gap or ionizing electrodes. A window or iris functioned to input the incident electromagnetic energy.
The patent entitled, "Variable Microwave Phase Shifter Utilizing A Plasma Electrode", issued Feb. 15, 1966 as U.S. Pat. No. 3,235,768, to H. Magnuski. This patent is for a device operable to shift the phase of microwaves in a waveguide. This electronic microwave phase shifter was operable to rapidly shift the phase of microwaves not unlike a "electronic on/off switch" for a waveguide. The ionization of gas in the waveguide by electrodes reflected the input signals either changing their phase or attenuating them. However this claimed device did not utilize the concepts of; a passive, radioactive, broad band discharge over bevelled fins.
A gas filled, electrical discharge device, or "transmit/receive switch", as used in radar at ultra short wave, for example, 3,000 mega cycles protecting a receiver from pulse feedback during transmission and operable over a wide range of incident ratio frequency power levels was the patent issued to J. D. Woermbke. This U.S. Pat. No. 3,268,757, issued Aug. 23, 1966 entitled, "Electrical Discharge Device", claimed an envelope structure with a discharge gap and gaseous atmosphere of chloride or helium, neon, argon, krypton, xenon, or radon all combined with iodine as operable to provide a "transmit/receive switch." However, this device unlike the subject invention did not claim the concept of a broad band, radioactive primed finned discharge gap. This "Electrical Discharge Device", patent to J. D. Woermbke is commonly assigned to the same assignee as this subject invention.
U.S. Pat. No. 4,027,255 dated May 31, 1977 entitled, "Fast Recovery Time Receiver Protector For Radars" as issued to Blakeney, described a waveguide type multi-stage receiver protector, wherein a chlorine gas discharge stage, combined with a radioactive primer device to provide a "transmit/receive switch" for pulse Doppler radar. The Blakeney device claimed a multi-stage passive receiver protector operable to protect radar receivers operating in a waveguide. The multi-stages comprised; a halogen gas discharge stage, a rapid start-up gas discharge with short recovery period, and a operational radioactive primer substrate. The radioactive primer was operable to provide the free electrons for initiating the gas discharge. However, discharge occurred throughout the multiplicity of successive stages.
The fin-line transmission line, is a preferred medium for millimeter wave radar applications because of its low insertion loss, wide band characteristics and the physically realizable circuits that are available at high frequencies. The configuration of a typical fin-line transmission line consists of; a low dielectric substrate material or sheet of narrow thickness having two metal "fins" printed on either side of the substrate. When the fins which are metallized on one side of the substrate it is referred to as a unilateral fin-line transmission line. While "fins" printed on both sides of the substrate material are considered a bilateral fin-line transmission line. In either embodiment, the fins should be separated by a narrow gap and grounded by enclosing the substrate sheet in a conventional rectangular waveguide enclosure.
Fin-line devices which are symmetrically mounted within the waveguide have conventional input and output ports using fin-line to waveguide transitions. Fin-line device performance is characterized in terms of the frequency band of the respective waveguide band in which the device operates, for example, Ka-band or Q-band. The microwave region is approximately 0.5-30GHz, while millimeter wave is considered greater than 30 GHz.
In the millimeter wave band range, no device was found as prior art which successfully achieved the protection from high peak powers and low insertion loss over a full waveguide band using a wide band plasma stage device.
This device should be used as a front, high power, gas plasma stage in a hybrid gas diode, receiver protector, for millimeter wave radar systems. Further this device should offer a simple circuit configuration providing lower fabrication costs in lot production because of the minimization of the number of stages.